1. Field of the invention
The present invention relates to wireless communication and, more particularly, to a dynamic frequency selection method in a Wireless Local Area Network (WLAN) system and an apparatus for supporting the same.
2. Related Art
With the recent development of information communication technology, a variety of wireless communication techniques are being developed. From among them, a Wireless Local Area Network (WLAN) is a technique for wirelessly accessing the Internet at homes or companies or in specific service providing areas by using portable terminals, such as a Personal Digital Assistant (PDA), a laptop computer, and a Portable Multimedia Player (PMP), based on wireless frequency technology.
A lot of standardization tasks are being performed since Institute of Electrical and Electronics Engineering (IEEE) 802 (i.e., the standardization organization of WLAN technology) was established on February, 1980. WLAN technology initially supported a speed of 1 to 2 Mbps through frequency hopping, band spreading, and infrared communication by using a frequency of 2.4 GHz according to IEEE 802.11, but recently may support a maximum speed of 54 Mbps by using Orthogonal Frequency Division Multiplexing (OFDM). In addition, in IEEE 802.11, standardizations for various techniques, such as the improvement of Quality of Service (QoS), Access Point (AP) protocol compatibility, security enhancement, radio resource measurement, wireless access vehicular environments, fast roaming, a mesh network, interworking with an external network, and wireless network management, are being put to practical use or developed.
In IEEE 802.11, IEEE 802.11b supports a maximum communication speed of 11 Mbps while using a frequency of a 2.4 GHz band. IEEE 802.11a commercialized after IEEE 802.11b has further reduced an influence on interference as compared with the frequency of a very confused 2.4 GHz band by using a frequency of a 5 GHz band not the 2.4 GHz band and has improved the communication speed up to a maximum of 54 Mbps using OFDM technology. However, IEEE 802.11a is disadvantageous in that it has a shorter communication distance than IEEE 802.11b. Furthermore, IEEE 802.11g has been in the spotlight considerably because it implements a maximum communication speed of 54 Mbps using the frequency of a 2.4 GHz band and satisfies backward compatibility like IEEE 802.11b. IEEE 802.11a has the advantage over IEEE 802.11a in the communication distance.
Furthermore, in order to overcome a limit to the communication speed that was considered as being weakness in the WLAN, IEEE 802.11n has recently been established as a technical standard. An object of IEEE 802.11n is to increase the speed and reliability of a network and to extend the coverage of a wireless network. More particularly, in order to support a High Throughput (HT) having a maximum data processing speed of 540 Mbps or higher, minimize an error in transmission, and optimize the data speed, IEEE 802.11n is based on Multiple Inputs and Multiple Outputs (MIMO) technology using multiple antennas on both sides of a transmitter and a receiver. Furthermore, this standard may use not only a coding scheme for transmitting several redundant copies in order to increase data reliability, but also Orthogonal Frequency Division Multiplex (OFDM) in order to increase the speed.
As the WLAN is actively propagated and applications employing the WLAN are diversified, there is a recent need for a new WLAN system for supporting a throughput higher than the data processing speed supported by IEEE 802.11n. A Very High Throughput (VHT) WLAN system is one of IEEE 802.11 WLAN systems which are recently proposed in order to support a data processing speed of 1 Gbps or higher
In IEEE 802.11 TGac that performs the standardization of the VHT WLAN system, active research is being carried out on a scheme using 8×8 MIMO and a channel bandwidth of 80 MHz or higher in order to provide the throughput of 1 Gbps or higher.
If the channel bandwidth of 80 MHz or higher is used, however, interference with other users using the channel bandwidth of 80 MHz or higher may become serious. In order to overcome this problem, a user using the channel bandwidth of 80 MHz or higher must be first protected, or the use of the channel bandwidth may be limited depending on conditions of a relevant frequency band according to regulations that must be observed when using the relevant frequency band.
In order for the relevant frequency band to be used in this environment, there is a need for a procedure of checking the relevant frequency band in order to protect a user having priority for the relevant frequency band or to satisfy administrative/policy regulations. A Dynamic Frequency Selection (DFS) method of adaptively adjusting the bandwidth of a channel or switching a channel may be used depending on the result of the check. In a method of checking the state of a channel (i.e., a precondition for the DFS procedure), an efficient method of minimizing the consumption of radio resources that may occur when a channel having a wide bandwidth is a target needs to be taken into consideration.